Follow this tip and I bet your oil consumption will drop: Do NOT fill to or above the Max mark. Only fill to about half way between the Min and Max marks.
And switch to M1 0W-40 or 15W-50 as Bud suggested. I've found higher consumption with M1 0W-30 (and it's not approved by MB).
I've also found much, much lower consumption with Schaefer Supreme 7000 20W-50 synthetic. Seems to be a great oil, if you can find it.